Cannot get signal on MCO2 output when PLLI2SR is used as MUX input on STM32F769IGT6

[DKotl]

I found that MCO2 output when derived from PLLI2SR doesn't work on STM32F769IGT6. I've selected as HSE input 10 MHz xtal that is running fine and using the following clock configuration (.ioc can be found in attachment):

Why is that? I didn't find so far that PLLI2SR cannot be used as a source, neither CubeMX report any error or warning. I'd like to use 25 MHz as clock for Ethernet PHY instead of deploying additional xtal/xco. Is it possible that CubeMX didn't provide all required code for initialization?

[waclawek.jan]

Read out and check/post the relevant RCC registers content.

JW